1. Field of the Invention
This invention relates to a crystallizer and method for casting using the same, mainly in casting of middle and low melting point metals, such as aluminum, magnesium, copper and tin, and their alloy, in particular for use in bottom or bottomless tubular casting of these metal castings, especially in casting of aluminum pistons.
2. Description of the Prior Art
In metal casting, rapid, bottom-top, sequential crystallization is an ideal mode of crystallization. If it is possible to complete the casting crystallization in this way, there is almost zero defects in the resulting casting. The external condition for achieving the rapid, bottom-top, sequential crystallization is the rapid, bottom-top (thermal current goes from top to bottom), sequential thermal diffusion. Therefore, the rapid, bottom-top, sequential thermal diffusion is a process much sought after by casting technicians worldwide. However, the rapid, bottom-top, sequential thermal diffusion can be achieved with very few existing casting technologies, such as electroslag remelting, ingot continuous casting, molten tin infusion process, etc. These technologies have their evident limitations. Those of electroslag remelting and ingot continuous casting are only capable of producing ingot with unvaried shape of cross section, and incapable of making casting of varied shapes. Products made with the molten tin infusion process are so expensive that the process cannot be put into wide industrial application.
The Chinese patent application CN1098344A has disclosed “a device for casting film metal mould and method for casting using the same”, with its configuration as shown in FIG. 25, which comprises a flask 90 , a film metal mould 91 , a spraying nozzle 92 , a pull bar 93 and a roof plate 94. This technology has realized the film mould casting, by using spraying nozzle 92 to spraying cooling medium from bottom to top on the outer wall of film metal mould 91 to perform rapid, from bottom to top, sequential thermal diffusion of casting 88 so as to guide the crystallization interface 89 to progress rapidly from bottom to top. Undoubtedly, this technology plays a positive role in making the process mature for the rapid, bottom-top, sequential thermal diffusion of casting. But it has its own drawbacks: (1) With the spaying method to cool down, the accuracy to control the moving speed of casting crystallization interface is not so precise that the internal quality of casting is still not satisfied. (2) The method of butt resistance welding to weld a plurality of pull bars 93 onto the outer wall of the film metal mould 91 , and the other end of the pull bar is fixed on the overall supporter, i.e., flask 90 , and film metal mould 91 is fixed through pulling force of the pull bars 93 and the resistance force of roof plate 94 . With few supporting points and uneven force on film metal mould, this way of fixing is apt to cause a large area of deformation; and the film metal mould is difficult to disassemble and assemble. These drawbacks call for urgent improvement.